Well, think about it from a biological standpoint. Women are sorta pre-wired from the factory to raise and nurture, it's been a successful blueprint for survival for along time running. Once the kids are grown up and out of the house those nurturing proclivities seek a re-purposing...or other such similar circumstances.

*caveat*

I'm not saying that barefoot and preggers is the proper or correct path for everyone. I'm simply referencing what has typically been the norm for humanity.